Fanzine going gaga over leftists’ leader with upper-class complaint (9)

I believe the answer is:

influenza

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'complaint' is the definition.
(influenza is a kind of disease)

I don't understand the remainder of the clue.

(Other definitions for influenza that I've seen before include "respiratory ailment" , "Common infection" , "Viral complaint" , "Nasty viral disease, usually of winter" , "Highly infectious viral disease" .)

I've seen this clue in The Hindu.

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